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	<title>YUI Library Examples: YAHOO Global Object: User Agent Detection</title>
    

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<!--begin custom header content for this example-->
<style type="text/css">
    #dd1,#dd2 {
        position: relative;
        margin: 1em 1em 0;
        width: 175px;
        float: left;
        cursor: move;
    }

    #demo p {
        position: relative;
        padding: 1em;
        height: 100%;
        margin: 0;
        font-weight: bold;
        text-align: center;
        z-index: 20;
    }

    #dd1 p {
        border: 10px solid #ccc;
        background-color: #eee;
    }

    #dd2 p {
        border: 10px solid #e76300;
        background-color: #fff5df;
    }

    #demo .shim {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        margin: 0;
        padding: 0;
        border: 0;
        z-index: 10;
    }
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<script type="text/javascript">
//enable passthrough of errors from YUI Event:
if ((typeof YAHOO !== "undefined") && (YAHOO.util) && (YAHOO.util.Event)) {
	YAHOO.util.Event.throwErrors = true;
}
</script>
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<body id="yahoo-com" class="yui-skin-sam">
<div id="custom-doc" class="yui-t2">
<div id="hd">
	<div id="ygunav">
		<p><em><a href="http://developer.yahoo.com/yui/">YUI Library Home</a></em></p>
		<form action="http://search.yahoo.com/search" id="sitesearchform">
		<input name="vs" type="hidden" value="developer.yahoo.com">
		<input name="vs" type="hidden" value="yuiblog.com">
		<div id="sitesearch">
			<label for="searchinput">Site Search (YDN &amp; YUIBlog): </label>
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			<input type="submit" value="Search" id="searchsubmit" class="ygbt">
		</div>
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	<div id="pagetitle"><h1>YUI Library Examples: YAHOO Global Object: User Agent Detection</h1></div>
</div>
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		  <div class="yui-ge">
			  <div class="yui-u first example">

    
	<div class="promo">
	<h1>YAHOO Global Object: User Agent Detection</h1>
	
	<div class="exampleIntro">
	<p>This example demonstrates the use of <code>YAHOO.env.ua</code> to identify the user's browser and to branch JavaScript logic based on what browser is being used.  (<strong>Note:</strong> We strongly recommend using feature detection rather than user-agent sniffing to fork code; only use this technique where it is absolutely necessary to do so &mdash; for example, in cases where browsers do not report their own capabilities accurately.)</p>
			
	</div>	
					
	<div class="example-container module ">
			<div class="hd exampleHd">
			<p class="newWindowButton yui-skin-sam"><!--<span id="newWindowLinkx"><span class="first-child">--><a href="yahoo_ua_detection_clean.html" target="_blank">View example in new window.</a><!--</span></span>-->		
		</div>		<div id="example-canvas" class="bd">
	
		
	<!--BEGIN SOURCE CODE FOR EXAMPLE =============================== -->
	
	<div id="demo">

    <select name="foo">
        <option value="NONE" selected="selected">This is a very long select element for the example</option>
        <option value="1">Apple</option>
        <option value="2">Rutabaga</option>
        <option value="3">Motor oil</option>
    </select>

    <hr>
    <div id="dd1">
        <p>
            NO IFRAME<br>
            Drag over the select
        </p>
    </div>

    <div id="dd2">
        <p>
            IFRAME<br>
            Drag over the select
        </p>
    </div>

</div>
<script type="text/javascript">
YAHOO.util.Event.onDOMReady(function () {
    var dd1 = new YAHOO.util.DD('dd1');
    var dd2 = new YAHOO.util.DD('dd2');

    dd1.startDrag = function (x,y) {
        YAHOO.log("Drag started for element with no protection from the display bug", "info", "example");
    }

    if (YAHOO.env.ua.ie > 5 && YAHOO.env.ua.ie < 7) {

        // Create an iframe shim
        var shim = document.createElement('iframe');
        shim.src = 'about:blank';
        shim.className = 'shim';

        // Add the shim to the dragging element on the first startDrag
        dd2.startDrag = function (x,y) {
            var d = this.getEl();

            if (d.firstChild !== shim) {
                YAHOO.util.Dom.setStyle(shim, 'height',d.offsetHeight);
                d.insertBefore(shim, d.firstChild);

                YAHOO.log("Your browser is IE " + YAHOO.env.ua.ie + ".  Shim added.", "info","example");

            } else {
                YAHOO.log("Your browser is IE " + YAHOO.env.ua.ie + ", but the shim was already added", "info","example");
            }
        }

    } else { // Not shim worthy

        dd2.startDrag = function (x,y) {
            YAHOO.log("Your browser is NOT IE.  No shim added.", "info", "example");
        }
    }
});
</script>
	
	<!--END SOURCE CODE FOR EXAMPLE =============================== -->
	
		
		</div>
		
	
	</div>			
	</div>
		
	<h2 class="first">First, a word of caution</h2>

<p><strong>Please DO NOT use this in place of feature detection</strong>.  Though many browsers have known JavaScript implementation quirks, it is bad practice and unsafe coding to make the assumption that because the page is being viewed in browser X that you can rely on feature Y being available.  Check for feature Y if you need it.</p>

<p>Browser sniffing is an imprecise science, and relies on many things in the browser environment to be just right.  Though many techniques are very accurate, 100% accuracy can't be guaranteed.</p>

<p>Use the <code>YAHOO.env.ua</code> object to inform you of what browser your page is being viewed in, but for your own sake, do not infer anything from this.</p>

<h2>What YAHOO.env.ua looks like</h2>

<p><code>YAHOO.env.ua</code> is an object literal containing keys for most major user agents.  The key corresponding to the current browser is assigned a version number.  All others have value 0.</p>

<textarea name="code" class="JScript" cols="60" rows="1">
if (YAHOO.env.ua.gecko > 0) {}  // e.g. Firefox
if (YAHOO.env.ua.ie > 0) {}     // Microsoft Internet Explorer

// Or leverage boolean coercion -- 0 evaulates as false
if (YAHOO.env.ua.opera) {}  // Opera
if (YAHOO.env.ua.webkit) {} // Safari, Webkit
</textarea>

<p>There's more information on the <code>YAHOO.env.ua</code> object and value ranges in the <a href="http://developer.yahoo.com/yui/docs/YAHOO.env.ua.html">API Documentation</a>.</p>

<h2>Bundled with the YAHOO Global Object</h2>

<p>YAHOO.env comes bundled with the <a href="http://developer.yahoo.com/yui/yahoo/">YAHOO Global Object</a> and is used to keep track of what is known about the YUI library and the browsing environment.</p>

<p>If you are using any other YUI component on your page, you should already have YAHOO.env available.  Otherwise, add the following:</p>

<textarea name="code" class="HTML" cols="60" rows="1">
<script type="text/javascript" src="http://yui.yahooapis.com/2.9.0/build/yahoo/yahoo-min.js"></script>

</textarea>

<h2>The example: drag elements and rendering bugs</h2>

<p>In this example, we'll add an iframe shim to a <a href="http://developer.yahoo.com/yui/dragdrop/">Drag and Drop</a> element to account for a known display bug in Internet Explorer 6 regarding the z-indexing of <code>select</code> elements.  For you folks out there not using IE6, here's a screen shot of the bug in action.</p>

<img src="<?= $assetsDirectory ?>/needs_shim.png" alt="IE6 shows the select above all elements despite z-indexing">

<p>In this case, there is no way other than browser sniffing or conditional comments to address IE's rendering bug.  We'll choose sniffing over using proprietary extensions.</p>

<p>Here's the markup for the example:</p>
<textarea name="code" class="HTML" cols="60" rows="1">
<div id="demo">

    <select name="foo">
        <option value="NONE" selected="selected">This is a very long select element for the example</option>
        <option value="1">Apple</option>
        <option value="2">Rutabaga</option>
        <option value="3">Motor oil</option>
    </select>

    <hr>

    <div id="dd1">
        <p>
            NO IFRAME<br>
            Drag over the select
        </p>
    </div>

    <div id="dd2">
        <p>
            IFRAME<br>
            Drag over the select
        </p>
    </div>

</div>
</textarea>

<h2>Targeting a browser for certain action</h2>
<p>Here, we create two Drag and Drop elements, then add the shim to the <code>dd2</code> element if the page is being viewed in a vulnerable version of IE.  Normally, of course, you'd add the shim behavior to both, but this will allow us to compare results.</p>

<textarea name="code" class="JScript" cols="60" rows="1">
YAHOO.util.Event.onDOMReady(function () {

    var dd1 = new YAHOO.util.DD('dd1');
    var dd2 = new YAHOO.util.DD('dd2');

    // Note the ua.{key} value must be above 0 to indicate a match
    if (YAHOO.env.ua.ie > 5 && YAHOO.env.ua.ie < 7) {

        // Create an iframe shim
        var shim = document.createElement('iframe');
        shim.src = 'about:blank';
        shim.className = 'shim';

        // Add the shim to the dragging element on the first startDrag
        dd2.startDrag = function (x,y) {
            var d = this.getEl();

            if (d.firstChild !== shim) {
                YAHOO.util.Dom.setStyle(shim, 'height',d.offsetHeight);
                d.insertBefore(shim, d.firstChild);

            }
        }
    }
});
</textarea>

<h2>Configuration for This Example</h2>

<p>You can load the necessary JavaScript and CSS for this example from Yahoo's servers.  <a href="http://developer.yahoo.com/yui/articles/hosting/?event&dom&dragdrop&MIN#configure">Click here to load the YUI Dependency Configurator with all of this example's dependencies preconfigured</a>.</p>

				</div>
				<div class="yui-u">
						<div id="loggerModule" class="yui-skin-sam">
						<h3 class="firstContent">YUI Logger Output:</h3>
								<div id="loggerGloss"><p><strong>Note:</strong> Logging and debugging is currently turned off for this example.</p> 
							<p class="loggerButton"><span id="loggerLink"><span class="first-child"><a href="yahoo_ua_detection_log.html">Reload with logging<br />
	 and debugging enabled.</a></span></span></p></div>
	
						</div>
					
				
					<div id="examples">
						<h3>YAHOO Global Object Examples:</h3>
	
						<div id="exampleToc">
							<ul>
								<li><a href='../yahoo/yahoo_type_checking.html'>Type-Checking Your Data</a></li><li class='selected'><a href='../yahoo/yahoo_ua_detection.html'>User Agent Detection</a></li><li><a href='../yahoo/yahoo_extend.html'>Creating Class Hierarchies with <code>YAHOO.lang.extend</code></a></li><li><a href='../yahoo/yahoo_augment_proto.html'>Creating a Composition-Based Class Structure Using <code>YAHOO.lang.augmentProto</code></a></li><li><a href='../yahoo/yahoo_augment_object.html'>Add Behavior to Objects or Static Classes with <code>YAHOO.lang.augmentObject</code></a></li><li><a href='../yahoo/yahoo_merge.html'>Combining Simple Data Sets with <code>YAHOO.lang.merge</code></a></li>							</ul>
						</div>
					</div>
					
					<div id="module">
						<h3>More YAHOO Global Object Resources:</h3>
						<ul>
							<li><a href="http://developer.yahoo.com/yui/yahoo/">User's Guide</a> (external)</li>
						<li><a href="../../docs/module_yahoo.html">API Documentation</a></li>
</ul>
					</div>
			  </div>
		</div>
		
		</div>
	</div>


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